Power tools used for applying pressure to a workpiece, for example in the insertion of hardware items into sheet material, can be hazardous to the operator and may enable the workpiece to occasionally become bent or otherwise damaged or, in the alternative, have insufficient clearance to allow large sized workpieces to be quickly and easily introduced and removed from the press. Another deficiency results from the large size of the hydraulic ram and associated pumping equipment required for long stroke operation previously used. To overcome these deficiencies, it has been previously proposed to provide various safety features for the prevention of accidents. For example, safety switches are often used to detect the presence of foreign objects or the hands, somedtimes with dual operating switches which require the placement of one hand on each switch to operate the press. While this is effective, the hands are unavailable to assist the operation, for example in holding the workpiece at its edges, and it well-known that safety switches are sometimes by-passed or otherwise turned off with some kind of cheating device.
In view of these deficiences of the prior art, it is one object of the invention to provide an improved safety power tool providing ample clearance of several inches for the insertion and removal of the workpieces while benefiting from the use of a short stroke ram with a typical stroke of about 174". Another object is to provide safe operation by providing means which will inherently prevent the application of substantial pressure to objects that are many more that typically 174" in thickness. A further object is to provide a safety power tool suited for use as a hardward insertion press which will travel a major portion, e.g., 75% of its stroke with only a slight pressure such as one pound or less, then travel the remaining fraction of its stroke at a much higher pressure, e.g., 4,000 lbs., so that the possibility of injury is avoided when the punch moves from its open position toward the closed position to a point where it is in contact or almost in contact with the workpiece. It is also an object of the invention to provide a highly effective means for raising the punch quickly to a retracted position and allowing it to fall to an operating position under the influence of gravity as well as for effectively sensing and controlling the motion of moving parts so that the press operaing ram will function only when desired to assure safe operation.